Belt driving device having a belt shift correcting member

Abstract

A belt driving device in which an endless belt is spanned around a drive pulley and a driven pulley and the belt is driven by rotation of the drive pulley includes a belt shift correcting member for correcting shifting of the endless belt. When the endless belt is shifted towards one side in an axial direction of one of the drive pulley and the driven pulley, the belt shift correcting member increases an angle of a circumference of the one of the drive and driven pulleys contacting a width-wise end part of the endless belt at the one side such that the angle of the circumference of the one of the drive and driven pulleys contacting the width-wise end part of the endless belt at the one side is larger at a part of the one of the drive and driven pulleys contacting an edge part of the width-wise end part of the endless belt than at other parts of the one of the drive and driven pulleys contacting other parts of the width-wise end part of the endless belt, and the angle of the circumference of the one of the drive and driven pulleys contacting the width-wise end part of the endless belt decreases toward a part of the one of the drive and driven pulleys contacting a width-wise center part of the endless belt. Furthermore, a coefficient of friction relative to the endless belt is made higher at a circumferential surface of an axial end part of the one of the drive and driven pulleys, which comes in contact with the width-wise end part of the endless belt at the one side in the axial direction of the one of the drive and driven pulleys, than at a circumferential surface of an axial center part of the one of the drive and driven pulleys.

I claim: 
     
       1. A belt driving device, comprising: a drive pulley;   a driven pulley;   an endless belt which spans around the drive pulley and the driven pulley and which is driven by rotation of the drive pulley; and   a belt shift correcting member which, when the endless belt is shifted toward one side in an axial direction of one of the drive pulley and the driven pulley, increases an angle of a circumference of said one of the drive and driven pulleys contacting a width-wise end part of the endless belt at said one side in the axial direction of said one of the drive and driven pulleys such that the angle of the circumference of said one of the drive and driven pulleys contacting said width-wise end part of the endless belt at said one side in the axial direction of said one of the drive and driven pulleys is larger at a part of said one of the drive and driven pulleys contacting an edge part of said width-wise end part of the endless belt than at other parts of said one of the drive and driven pulleys contacting other parts of said width-wise end part of the endless belt and said angle of the circumference of said one of the drive and driven pulleys contacting said width-wise end part of the endless belt decreases toward a part of said one of the drive and driven pulleys contacting a width-wise center part of the endless belt,   wherein a coefficient of friction of said one of the drive and driven pulleys relative to the endless belt is higher at a circumferential surface of an axial end part thereof, which comes in contact with said width-wise end part of the endless belt at said one side in the axial direction of said one of the drive and driven pulleys, than at a circumferential surface of an axial center part of said one of the drive and driven pulleys.   
     
     
       2. The belt driving device of claim 1, wherein the belt shift correcting member comprises a belt shift correcting roller which is rotatably arranged upstream of said one of the drive and driven pulleys in a belt driven direction such that the belt shift correcting roller contacts and presses a surface of the width-wise end part of the endless belt at said one side in the axial direction of said one of the drive and driven pulleys so as to bend the width-wise end part of the endless belt. 
     
     
       3. The belt driving device of claim 2, wherein the belt shift correcting roller has a rotational axis substantially parallel to said one of the drive and driven pulleys and is tapered toward the width-wise center part of the endless belt. 
     
     
       4. The belt driving device of claim 2, wherein the belt shift correcting roller comprises a needle shaped roller which is inclined such that the angle at a circumference of said one of the drive and driven pulleys contacting the endless belt increases at a part of said one of the drive and driven pulleys contacting said width-wise end part of the endless belt at said one side in the axial direction of said one of the drive and driven pulleys. 
     
     
       5. The belt driving device of claim 2, wherein the belt shift correcting member comprises an umbrella shaped roller having a rotational axis perpendicular to said one of the drive and driven pulleys and an outer circumferential surface tapered such that the angle at a circumference of said one of the drive and driven pulleys contacting the endless belt increases at a part of said one of the drive and driven pulleys contacting said width-wise end part of the endless belt at said one side in the axial direction of said one of the drive and driven pulleys. 
     
     
       6. A belt driving device, comprising: a drive pulley;   a driven pulley;   an endless belt which spans around the drive pulley and the driven pulley and which is driven by rotation of the drive pulley; and   a belt shift correcting member having a belt shift correcting surface, the belt shift correcting surface has an angle, the angle slopes from a first position to a second position, where the second position is located farther away from a width-wise center part of the endless belt along an axial direction of one of the drive pulley and the driven pulley than does the first position, and where the first position is located on one side of a thickness-wise center part of the endless belt and the second position is located on another side of the thickness-wise center part of the endless belt,   wherein the belt shift correcting surface of the belt shift correcting member contacts a width-wise end part of the endless belt, and   wherein a coefficient of friction of said one of the drive and driven pulleys relative to the endless belt is higher at a circumferential surface of an axial end part thereof than at a circumferential surface of an axial center part of said one of the drive and driven pulleys.   
     
     
       7. The belt driving device of claim 6, wherein the belt shift correcting member comprises a belt shift correcting roller which is rotatably arranged upstream of said one of the drive and driven pulleys in a belt driven direction such that the belt shift correcting roller contacts and presses a surface of the width-wise end part of the endless belt at said one side in the axial direction of said one of the drive and driven pulleys so as to bend the width-wise end part of the endless belt. 
     
     
       8. The belt driving device of claim 7, wherein the belt shift correcting roller has a rotational axis substantially parallel to said one of the drive and driven pulleys. 
     
     
       9. The belt driving device of claim 7, wherein the belt shift correcting roller comprises a needle shaped roller. 
     
     
       10. The belt driving device of claim 7, wherein the belt shift correcting member comprises an umbrella shaped roller.